The present invention relates to a determination of sulfurous acid, especially a small amount of sulfurous acid, in liquids and an apparatus therefor. More particularly, the present invention relates to a novel, simple and speedy determination of sulfurous acid based on the Modified Rankine's method, which has been adopted in Japanese Health and Medical Laboratories, and an apparatus therefor.
Sulfurous acid and sulfites are generally used for foods as a bleaching or a discoloration inhibitor. They are employed in the production of cornstarch as an antiseptic and a stimulator for starch purification. They are also used for the sterilization of vessels, preservation of fresh fruit juices and regulation of fermentation processes in the production of wines. They are also employed in the fumigation of dry fruits.
A maximum amount of sulfurous acid and sulfites remaining in foods treated with sulfurous acid and sulfites is provided in the Japanese Food Hygiene Regulations in detail. For example, the amount of sulfurous acid or sulfites remaining in dried gourd shavings must be less than 5,000 ppm as sulfur dioxide, that in dried apricots and dried peaches less than 2,000 ppm, that in powdered Konnyaku (jellied extract from arum tree) less than 900 ppm, that in wines less than 350 ppm and that in general foods less than 30 ppm. Sulfurous acid and sulfites are prohibited for use with sesames, beans and vegetables.
Since people have taken an increasing interest in food sanitation, nowadays, the amount of and kinds of food additives have become severely limited. Food manufacturers must control the sulfurous acid content remaining in final products within a statutory standard when they use sulfurous acid or sulfites in the food manufacturing process. Thus, they are required to determine an amount of sulfurous acid remaining in foods and conduct process control.
For determination of a slight amount of sulfurous acid remaining in foods, the Modified Monnier-Williams method, the distilled iodine method, the Colorimetric method, the microdiffusion method, the Modified Rankine's Alkaline Titration method, the Modified Rankine's Colorimetric method, gas chromatography, etc. have been used. These methods require particular apparatus, a great deal of skill and a long period of time for determination of sulfurous acid. In addition, automatic determination cannot be adopted by these methods in principle.